1. Field of the Invention
The present invention relates to a photocathode, an electron tube, a field assist type photocathode, a field assist type photocathode array, and a field assist type electron tube.
2. Related Background Art
There is a conventionally known apparatus in which an optical filter is disposed on a light entrance surface of a photocathode, for example as described in Patent Document 1, for the purpose of detecting light of a specific wavelength. In this apparatus, when light is incident to the optical filter, the optical filter filters out light of the wavelengths other than the specific wavelength included in the incident light. The photocathode absorbs the light of the specific wavelength transmitted by the optical filter, to generate photoelectrons (e−).
A known photocathode of an electric-field-assisted type (which is called a field assist type) is one consisting of a stack of a substrate, a photon absorbing layer (light absorbing layer) for generating photoelectrons, and an electron emitting layer for accelerating the photoelectrons generated in the light absorbing layer, for example, as described in Patent Document 1. In the photocathode described in Patent Document 1, contact pads (electrodes) are connected to the photon absorbing layer and to the electron emitting layer, respectively, and a bias voltage is applied between these contact pads. The electrons (photoelectrons) generated in the photon absorbing layer are accelerated by an electric field established in the photocathode according to the application of the bias voltage, and are emitted from the electron emitting layer.    [Patent Document 1] Japanese Patent Application Laid-open No. H6-34548